As the semiconductor industry has strived for higher device density, higher performance, and lower costs, problems involving both fabrication and design have been encountered. One solution to these problems has been the development of a fin-like field effect transistor (FinFET). A typical FinFET includes a thin vertical “fin” of semiconductor materials. The source, drain, and channel regions are defined within this fin. The transistor's gate is wrapped around the channel region of the fin, engaging it on both the top and the sidewalls of the fin. This configuration allows the gate to induce current flow in the channel from three sides. Thus, FinFET devices have the benefit of higher current flow and reduced short channel effects.
However, there are various challenges in fabricating FinFET devices. For example, ion implantation, traditionally used for doping planar devices, has been similarly used for doping FinFET devices to create lightly doped source/drain (LDD) regions (or source/drain extensions) in the fin. But due to its directional effect, ion implantation has been found quite ineffective in creating uniform dopant concentration in the three-dimensional fin. For example, top portions of a fin typically get much higher dopant concentration than its lower portions because the height of the fin typically exceeds the capability of the ion implanters. Tilted ion implantation is also not very effective for FinFET due to so-called shadowing effects where nearby structures (e.g., nearby fins, gates, and/or photoresist masking elements) block the path of the ions. Consequently, not all advantages of the FinFET devices are realized.